In a wireless communication system, various wireless communication devices communicate with each other over the air interface using the radio links. When a wireless communication device transmits a data packet to another wireless communication device and the receiving wireless communication device is able to correctly decode the received data packet, then the receiving wireless communication device sends a positive acknowledgement (ACK) to the wireless communication device transmitting the data packet. An ACK denotes to the transmitting wireless communication device that the data packet was received and correctly decoded by the receiving wireless communication device and the transmitting wireless communication device does not need to re-transmit the packet data.
Otherwise, when the receiving wireless communication device is not able to correctly decode the data packet, it sends a negative acknowledgement (NACK) to the wireless communication device transmitting the data packet and implicitly asks the transmitting wireless communication device to re-transmit the data packet. A NACK denotes to the transmitting wireless communication device that the data packet was not correctly received and decoded by the receiving wireless communication device and the transmitting wireless communication device needs to re-transmit the data packet. In such a scenario, the transmitting wireless communication device re-transmits the data packet.
With the above ACK/NACK techniques, there is a very high possibility that the receiving wireless communication device is again not able to correctly decode the re-transmitted data packet, as the transmitting wireless communication device has no information about the power needed for the re-transmission of the data packet such that the re-transmitted data packet can be correctly decoded by the receiving wireless communication device. Transmission errors may be reduced by transmitting at higher power levels. On the other hand, transmission at higher power levels consumes base station capacity and may interfere with other transmissions.
As a result, recent Hybrid Automatic Repeat ReQuest (H-ARQ) schemes attempt to allocate transmission power for the re-transmission data packet. One such scheme is a Boosted scheme, where the re-transmission data packet is always and each time transmitted with increased power. However, this scheme can result in an excessive number of re-transmissions until an appropriate power level is attained and/or a waste of transmission power. This scheme also increases the reverse noise, subsequently, decreasing the number of wireless communication devices that can be served by a particular base station. Another scheme is De-Boosted and Super De-Boosted scheme, where the re-transmission data packet is every time transmitted with decreased power. However, this scheme, too, can increase the average number of re-transmissions. Different combinations of the above two scheme are also used, but none of the methods solves the problem of determining an optimal power for re-transmission by the transmitting wireless communication device for an error free reception and correct decoding of the re-transmitted data packet while minimizing a number of re-transmissions.
Accordingly, there is a need for a method and apparatus for power control for the re-transmission data packet, in a wireless communication system.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.